1. Field of the Invention
The present invention relates to a current-perpendicular-to-the-plane (CPP) magnetic sensing element in which a sensing current flows in the thickness direction of each layer of the multilayer film. More particularly, the invention relates to a magnetic sensing element in which the sensing current is prevented from expanding in the track width direction in the multilayer film, enabling an improvement in read output, and to a method for fabricating the same.
2. Description of the Related Art
FIG. 14 is a partial sectional view which shows a structure of a conventional magnetic sensing element, viewed from the surface facing a recording medium.
A lower electrode layer 13 is composed of a NiFe alloy or the like. A first antiferromagnetic layer 3, a pinned magnetic layer 4, a nonmagnetic material layer 5, and a free magnetic layer 6 are deposited in that order on the lower electrode layer 13. A laminate including the first antiferromagnetic layer 3 to the free magnetic layer 6 is referred to as a multilayer film 11.
Second antiferromagnetic layers 7 are disposed on side regions 6a of the free magnetic layer 6, and insulating layers 12 are disposed on the second antiferromagnetic layers 7.
An upper electrode, layer 14 is disposed over the insulating layers 12 and the central region 6b of the free magnetic layer 6 exposed to a space between the second antiferromagnetic layers 7 in the track width direction (in the X direction in the drawing).
In the magnetic sensing element shown in FIG. 14, a track width Tw is defined by the distance in the track width direction between the lower surfaces of the second antiferromagnetic layers 7.
In the magnetic sensing element shown in FIG. 14, an exchange coupling magnetic field is generated between each second antiferromagnetic layer 7 and each side region 6a of the free magnetic layer 6, and the magnetization of the side, region 6a of the free magnetic layer 6 is pinned in the X direction. The magnetization of the central region 6b of the free magnetic layer 6 is aligned in the X direction by a bias, magnetic field due to an exchange interaction in the magnetic layer, and the magnetization of the central region 6b is rotated in response to an external magnetic field. A method in which the magnetization of the free magnetic layer 6 is controlled using the antiferromagnetic layers 7 as described above is referred to as an exchange bias method.
The conventional magnetic sensing element shown in FIG. 14 has a current-perpendicular-to-the-plane (CPP) structure in which the electrodes 14 and 13 are disposed on the upper and lower surfaces of the multilayer film 11 in the thickness direction (in the Z direction), and a sensing current flows in the thickness direction of each layer of the multilayer film 11.
In the magnetic sensing element shown in FIG. 14, the insulating layers 12 cover the second antiferromagnetic layers 7. By forming the insulating layers 12, it is possible to prevent the sensing current, which flows from the upper electrode layer 14 into the multilayer film 11, from being shunted to the second antiferromagnetic layers 7.
However, the magnetic sensing element shown in FIG. 14 has the following drawback. The sensing current flowing into the multilayer film 11 expands and flows wider than the track width Tw. As a result, the effective read track width which actually contributes to the magnetoresistance effect increases, resulting in side reading and a decrease in read output. In FIG. 14, expansion of the sensing current is indicated by the arrows.
In the magnetic sensing element shown in FIG. 14, the width in the track width direction of the multilayer film 11 is wider than the track width Tw, and no insulating layer is interposed between the lower electrode layer 13 and the first antiferromagnetic layer 3. Therefore, the sensing current is considered to expand in the track width direction, particularly, in the lower part of the multilayer film 11.
FIG. 15 is a partial sectional view which shows a structure of another conventional magnetic sensing element, viewed from the surface facing a recording medium. In the magnetic sensing element shown in FIG. 15, a recess 13a is formed in each side region 13b of a lower electrode layer 13, and an insulating layer 2 is formed in the recess 13a. A first antiferromagnetic layer 3 is disposed over the insulating layers 2 and a central region 13c of the lower electrode layer 13. As in the magnetic sensing element shown in FIG. 14, insulating layers 12 are disposed on second antiferromagnetic layers 7.
As shown in FIG. 15, in each side region, the antiferromagnetic layer 3 and the electrode layer 13 are insulated from each other and the antiferromagnetic layer 7 and the electrode layer 14 are insulated from each other. Expansion in the track width direction of the sensing current in the multilayer film 11 is considered to be suppressed compared to the structure of the magnetic sensing element shown in FIG. 14.
However, in the magnetic sensing element shown in FIG. 15, expansion of the sensing current in the multilayer film 11 is still not effectively prevented, and it is not possible to improve read output properly. In FIG. 15, the flow of the sensing current is indicated by the arrows.
In the structure shown in FIG. 15, although the antiferromagnetic layers 3 and 7 and the electrode layers 13 and 14 are insulated from each other by the insulating layers 2 and 12, respectively, the width in the track width direction (in the X direction) of the multilayer film 11 is larger than the track width Tw. When the thickness of the multilayer film is larger than the mean free path, in particular, in the sensing current flowing in the vicinity of each end of the track width Tw region, conduction electrons do not necessarily move in the Z direction and have a slight angular distribution. Therefore, the current expands. Scattering (including specular scattering) at the interfaces between the layers also causes expansion of the current.
As described above, the current tends to flow wider than the track width Tw in the multilayer film 11. Therefore, in the structure shown in FIG. 15, it is not possible to suppress the expansion of the effective track width more effectively so that side reading is prevented and read output is improved.
As described above, when the exchange bias method is employed, in the structure of the conventional magnetic sensing element shown in FIG. 14 or 15, it is not possible to prevent the sensing current from expanding in the track width direction in the multilayer film 11, resulting in a decrease in read output, etc. In particular, the problem described above becomes more obvious as the track is narrowed in order to meet higher recording densities.